Method and device for compressing image signal and endoscope system using such device

ABSTRACT

There is provided a method of compressing an image signal including a plurality of pixel signals outputted from a pixel array in which color pixels are arranged in a predetermined array. The method includes calculating a difference between pixel signals of neighboring same color pixels in the pixel array in accordance with predetermined order where the plurality of pixel signals are outputted from the pixel array, and generating a difference signal representing the calculated difference between the pixel signals of neighboring same color pixels.

BACKGROUND OF THE INVENTION

The present invention relates to a method and a device for compressingan image signal and an endoscope system using such a device.

Various types of methods and devices for compressing an image signalhave become widespread. Examples of such a device are disclosed inJapanese Patent Provisional Publications Nos. 2002-118764 (hereafter,referred to as JP2002-118764A) and 2003-244458 (hereafter, referred toas JP2003-244458A).

Recently, a technology for transmitting a signal (a packet) to adestination via a plurality of DST (Diffusive Signal-Transmission) chipshas been proposed as described in Japanese Patent ProvisionalPublication No. 2003-188882 and on a web site4“http://www.utri.cojp/venture/venture2.html” (retrieved in November,2005) by CELLCROSS Co., Ltd (the same contents are also available on thewebsite http://www.cellcross.co.jp/technology.html). Hereafter, such atechnology is referred to as a 2D-DST (two-dimensional DST) technology.Each DST chip is formed in a minute size for achieving flexibility of asubstrate in which DST chips are provided and reduction in thickness ofthe substrate. Such a limited size of each DST chip also limits thesignal processing performance and the memory size of each DST chip.Therefore, it is difficult to transmit the large amount of data to thedestination at a time through the DST chips. It is desirable that thedata to be transmitted is compressed and the compressed data istransmitted to the destination via the DST chips.

The technique disclosed in the JP2002-118764A and JP2003-244458Arequires relatively high signal processing performance and a relativelylarge memory size due to its complicated control. Therefore, to achievethe technique disclosed in the JP2002-118764A and JP2003-244458A usingthe DST chips, each DST chip needs to have relatively high signalprocessing performance and a relatively large memory size. However, asdescribe above, it is difficult for each DST chip to have relativelyhigh signal processing performance and relatively large memory size dueto its limited chip size. Therefore, it is difficult for each DST chipto have the technique disclosed in JP2002-118764A and JP2003-244458A.

Various image signal compression techniques such as a JPEG (JointPhotographic experts Group) compression technique have been proposed.However, such an image signal compression technique needs to use highprocessing performance and a frame memory. Therefore, it is difficultfor the DST chip to employ such an image signal compression technique,

SUMMARY OF THE INVENTION

The present invention is advantageous in that at least a method and adevice for compressing a signal without requiring relatively highprocessing performance and a relatively large amount of memory areprovided.

According to an aspect of the invention, there is provided a method ofcompressing an image signal including a plurality of pixel signalsoutputted from a pixel array in which color pixels are arranged in apredetermined array. The method includes calculating a differencebetween pixel signals of neighboring same color pixels in the pixelarray in accordance with predetermined order where the plurality ofpixel signals are outputted from the pixel array, and generating adifference signal representing the calculated difference between thepixel signals of neighboring same color pixels.

With this configuration, it is possible to effectively compress an imagesignal using a processing circuit having relatively low processingperformance and a relatively low memory amount.

In at least one aspect, the calculating the difference is performed foreach of the pixel signals outputted from the pixel array line by line.

In at least one aspect, the method further including addingidentification information concerning the difference signal to thedifference signal.

In at least one aspect, the pixel signals are outputted from the pixelarray in the predetermined order such that colors of neighboring pixelsignals successively outputted are different from each other

In at least one aspect, the predetermined array includes a Bayer array.

In at least one aspect, the calculating the difference and thegenerating the difference signal are repeated so that difference signalsare generated for all of the plurality of pixel signals of the pixelarray,

According to another aspect of the invention, there is provided a methodof compressing an image signal including a plurality of pixel signalsoutputted from a pixel array in which color pixels are arranged in apredetermined array. The method includes separating each of theplurality of pixel signals from the image signal in accordance withcolor, storing the separated pixel signals in accordance with color,calculating a difference between pixel signals of neighboring same colorpixels using the stored pixel signals, and generating a differencesignal representing the calculated difference between the pixel signalsof neighboring same color pixels.

With this configuration, it is possible to effectively compress an imagesignal using a processing circuit having relatively low processingperformance and a relatively low memory amount.

According to another aspect of the invention, there is provided a methodof compressing an image signal including a plurality of pixel signalsoutputted from a pixel array in which color pixels are arranged in apredetermined array. The method includes separating the plurality ofpixel signals from the image signal line by line, storing at least oneline of separated pixel signals, calculating a difference between pixelsignals in neighboring lines having a same color pixel arrangement usingthe stored at least one line of separated pixel signals, and generatinga difference signal representing the calculated difference between thepixel signals of neighboring same color pixels.

With this configuration, it is possible to effectively compress an imagesignal using a processing circuit having relatively low processingperformance and a relatively low memory amount.

According to another aspect of the invention, there is provided a methodof compressing an image signal including a plurality of pixel signalsoutputted from a pixel array in which color pixels are arranged in apredetermined array. The method includes separating the plurality ofpixel signals from the image signal line by line, storing at least oneline of separated pixel signals, calculating a difference between pixelsignals in a neighboring lines having a same color arrangement using thestored at least one line of separated pixel signals, and generating adifference signal representing the calculated difference if at least oneof difference signals calculated for all the pixel signals in the storedat least one line of separated pixel signals is not zero, and generatinga notification signal if all the difference signals calculated for allthe pixel signals in the stored at least one line of separated pixelsignals are zero.

With this configuration, it is possible to effectively compress an imagesignal using a processing circuit having relatively low processingperformance and a relatively low memory amount.

In at least one aspect, the notification signal indicates that all ofthe difference signals calculated for all the pixel signals in thestored at least one line of separated pixel signals are zero.

According to another aspect of the invention, there is provided a devicefor compressing an image signal including a plurality of pixel signalsoutputted from a pixel array in which color pixels are arranged in apredetermined array. The device is provided with a signal obtaining unitconfigured to obtain the image signal, a signal separation unitconfigured to separate each of the plurality of pixel signals from theimage signal in accordance with color, a plurality of memoriesrespectively storing different color pixel signals separated by thesignal separation unit in accordance with color, and a difference signalgeneration unit configured to calculate a difference between pixelsignals of neighboring same color pixels using the pixel signals storedin at least one of the plurality of memories and to generate adifference signal representing the difference.

With this configuration, it is possible to effectively compress an imagesignal using a processing circuit having relatively low processingperformance and a relatively low memory amount.

In at least one aspect, each of the memories is able to store at leasttwo neighboring pixel signals in the image signal.

In at least one aspect, the difference signal generation unit calculatesthe difference between pixel signals of neighboring same color pixelsfor all the plurality of pixel signals in the pixel array line by line.

In at least one aspect, the difference signal generation unit addsidentification information concerning the difference signal to thedifference signal.

In at least one aspect, the pixel array includes a Bayer array. In thiscase, the plurality of memories may include a first memory storing pixelsignals for red pixels in an odd line in the pixel array, a secondmemory storing pixel signals for green pixels in an odd line in thepixel array, a third memory storing pixel signals for green pixels in aneven line in the pixel array, and a fourth memory storing pixel signalsfor blue pixels in an even line in the pixel array.

In at least one aspect, the pixel array includes a Bayer array. In thiscase, the plurality of memories may include a first memory storing pixelsignals for red pixels in an odd line in the pixel array, a secondmemory storing pixel signals for green pixels in odd and even lines inthe pixel array, and a third memory storing pixel signals for bluepixels in an even line in the pixel array.

According to another aspect of the invention, there is provided a devicefor compressing an image signal including a plurality of pixel signalsoutputted from a pixel array in which color pixels are arranged in apredetermined array. The device is provided with a plurality of signalprocessing units respectively corresponding to different colors ofpixels in the pixel array. Each of the plurality of signal processingunits includes a signal obtaining unit configured to obtain the imagesignal, a signal extraction unit configured to extract pixel signalshaving a predetermined color from the image signal, and a differencesignal generation unit configured to calculate a difference betweenpixel signals of neighboring same color pixels using the pixel signalsextracted by the signal extraction unit and to generate a differencesignal representing the difference.

With this configuration, it is possible to effectively compress an imagesignal using a processing circuit having relatively low processingperformance and a relatively low memory amount,

According to another aspect of the invention, there is provided a devicefor compressing an image signal including a plurality of pixel signalsoutputted from a pixel array in which color pixels are arranged in apredetermined array. The device is provided with a signal obtaining unitconfigured to obtain the image signal, a signal separation unitconfigured to separate the plurality of pixel signals from the imagesignal line by line, a plurality of memories respectively storingdifferent lines of pixel signals separated by the signal separationunit, and a difference signal generation unit configured to calculate adifference between pixel signals in neighboring lines having a samecolor pixel arrangement using the pixel signals stored in at least oneof the plurality of memories and to generate a difference signalrepresenting the difference.

With this configuration, it is possible to effectively compress an imagesignal using a processing circuit having relatively low processingperformance and a relatively low memory amount.

According to another aspect of the invention, there is provided a devicefor compressing an image signal including a plurality of pixel signalsoutputted from a pixel array in which color pixels are arranged in apredetermined array. The device is provided with a signal obtaining unitconfigured to obtain the image signal, a signal separation unitconfigured to separate the plurality of pixel signals from the imagesignal line by line, a plurality of memories respectively storingdifferent lines of pixel signals separated by the signal separationunit, a difference calculation unit configured to calculate a differencebetween pixel signals in neighboring lines having a same color pixelarrangement the pixel signals stored in at least one of the plurality ofmemories, and a difference signal generation unit configured to generatea difference signal representing the calculated difference if at leastone of difference signals calculated for all the pixel signals of a linein the pixel array is not zero, and to generate a notification signal ifall difference signals calculated for all the pixel signals in a line inthe pixel array are zero.

With this configuration, it is possible to effectively compress an imagesignal using a processing circuit having relatively low processingperformance and a relatively low memory amount.

In at least one aspect, each of the plurality of memories is able tostore a line of pixel signals.

In at least one aspect, the pixel array includes a Bayer array. In thiscase, the plurality of memories includes a first line memory storingpixel signals in an odd line in the pixel array and a second line memorystoring pixel signals in an even line in the pixel array.

According to another aspect of the invention, thee is provided awearable device, which is provided with a substrate including aconductive sheet and a plurality of diffusive signal-transmission chipsdistributed over the conductive sheet. In this configuration, each ofthe plurality of diffusive signal-transmission chips comprises one ofthe above mentioned device. The conductive layer is formed to be able tocover at least a part of a body of a subject, and information on thebody of the subject is transmitted through the substrate.

With this configuration, it is possible to effectively compress theimage signal using DST chips having relatively low processingperformance.

According to another aspect of the invention, there is provided awearable device, which is provided with a substrate including aconductive sheet and a plurality of diffusive signal-transmission chipsdistributed over the conductive sheet. In this configuration, at leastparts of the plurality of diffusive signal-transmission chips form theabove mentioned device including the plurality of signal processingunits. The plurality of signal processing units are respectivelyprovided in different ones of the at least parts of the plurality ofdiffusive signal-transmission chips. The conductive layer is formed tobe able to cover at least a part of a body of a subject, and informationon the body of the subject is transmitted through the substrate.

With this configuration, it is possible to effectively compress theimage signal using DST chips having relatively low processingperformance.

According to another aspect of the invention, there is provided anendoscope system, which is provided with a capsule-type endoscope havinga form of a capsule, and one of the above mentioned wearable device. Thecapsule-type endoscope includes an image pickup unit configured toobtain an image of an inside of a body cavity of the subject and togenerate an image signal representing the obtained image, and a wirelesscommunication unit configured to transmit the image signal as a radiosignal. The signal obtaining unit in the wearable device includes anantenna which receives the image signal transmitted from the wirelesscommunication unit of the capsule-type endoscope.

With this configuration, it is possible to effectively compress theimage signal using DST chips having relatively low processingperformance,

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1 is a block diagram of an endoscope system according to a firstembodiment of the invention.

FIG. 2 is a block diagram of a capsule-type endoscope provided in theendoscope system.

FIG. 3 illustrates a color filter on which primary color filters arearranged in a so-called Bayer array.

FIG. 4 is a cross section of a diagnostic jacket illustrating astructure of layers of the diagnostic jacket,

FIG. 5 is a block diagram of a DST chip according to the firstembodiment.

FIG. 6 is a flowchart illustrating an image signal compression processexecuted by the DST chip according to the first embodiment.

FIG. 7 shows an image signal converted by an A-D converter in the DSTchip.

FIG. 8 is a flowchart illustrating a signal separation process executedin the image signal compression process.

FIGS. 9A to 9F are explanatory illustrations for explaining effect of adifference operation process executed in the image signal compressionprocess,

FIG. 10 is a block diagram of an endoscope system according to a secondembodiment of the invention.

FIG. 11 is a block diagram of a DST chip according to the secondembodiment.

FIG. 12 is a flowchart illustrating an image signal compression processexecuted by the DST chip according to the second embodiment.

FIG. 13 is a flowchart illustrating a signal extraction process executedin the image signal compression process shown in FIG. 12.

FIG. 14 is a block diagram of a DST chip according to the thirdembodiment.

FIGS. 15A to 15C are explanatory illustrations for explaining effect ofa difference operation process executed in an image signal compressionprocess according to a third embodiment.

FIG. 16 is a flowchart illustrating the image signal compression processexecuted by the DST chip according to the third embodiment.

FIG. 17 is a block diagram of a DST chip according to a fourthembodiment.

FIG. 18 is a flowchart illustrating the image signal compression processexecuted by the DST chip according to the fourth embodiment.

FIGS. 19A to 19C are explanatory illustrations for explaining the casewhere output values of pixel signals in targeted two lines are equal toeach other.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments according to the invention are described withreference to the accompanying drawings.

First Embodiment

FIG. 1 is a block diagram of an endoscope system 10 according to a firstembodiment of the invention. The endoscope system 10 is used to observethe inside of a body cavity of a subject 1 for medical diagnosticpurpose. As shown in FIG. 1, the endoscope system 10 includes acapsule-type endoscope 100, a diagnostic jacket (i.e., a wearabledevice) 200, and a PC (personal computer) 300 having a monitor. Thecapsule-type endoscope 100 is formed to be a small size endoscopecapable of getting into the inside of a body cavity for imaging theinside of the body cavity.

The diagnostic jacket 200 is worn by the subject 1 so that image dataoutput by the capsule-type endoscope 100 can be obtained. On the monitorof the PC 300, observation images can be displayed.

FIG. 2 is a block diagram of the capsule-type endoscope 100. Since thecapsule-type endoscope 100 is small and is formed in a shape of acapsule, the capsule-type endoscope 100 is able to get into an inside ofa meandering narrow long tube (e.g., a bowel) and to image the inside ofthe tube. As shown in FIG. 2, the capsule-type endoscope 100 includes apower supply unit 102, a control unit 104 for controlling thecapsule-type endoscope 100, a memory 106 in which various types of datais stored, an illumination units 108 for illuminating the inside of abody cavity, an objective optical system 110 for forming an image of theinside of a body cavity, a solid-state image pickup device 112, and anoutput unit 114 for outputting a radio wave, and an antenna 115 throughwhich a radio wave is transmitted or received.

When power of the capsule-type endoscope 100 is turned to ON and thecapsule-type endoscope 100 is inserted into a body cavity, thecapsule-type endoscope 100 illuminates the inside of the body cavitywith the illumination units 108. Light reflected from an inside wall ofthe body cavity enters the objective optical system 110, and theobjective optical system 100 forms an image on an image side focal plane(i.e., a light reception surface of the solid-state image pickup device112).

The solid-state image pickup device 112 which receives the image formedby the objective optical system 110 has n by m pixels arranged in amatrix (n pixels in a horizontal direction and m pixels in a verticaldirection) and is able to generate color images. The solid-state imagepickup device 112 has a color filter on the front side of the lightreception surface thereof. FIG. 3 illustrates the color filter on whichprimary color filters (i.e., R(red), G(green) and B(blue) filters) arearranged in a so-called Bayer array. More specifically, on each oddline, R and G filters are alternately arranged (i.e., arranged in a formof R, G, R, G . . . ). On each even line, G and B filters arealternately arranged (i.e., arranged in a form of G, B, G, B, . . . ).

The solid-state image pickup device 112 converts the image formedthereon to an electronic image signal. The control unit 104 controls theoutput unit 114 to modulate the image signal generated by thesolid-state image pickup device 112. Then, the modulated image signal istransmitted through the antenna 115 as a radio signal. The radio signal(i.e., an analog image signal) outputted by the capsule-type endoscope100 is received by the diagnostic jacket 200.

A configuration and operations of the diagnostic jacket 200 will now bedescribed. As shown in FIG. 1, the diagnostic jacket 200 is formed tocover a part of a body of the subject 1. A plurality of DST chips 230each of which is configured to transmit a signal based on the 2D-DSTtechnology are distributed over the diagnostic jacket 200. In thediagnostic jacket 200, a transmission channel for transmitting the imagesignal outputted by the capsule-type endoscope 100 can be formed withoutusing a metal pattern or a wired line. By employing the 2D-DSTtechnology, the diagnostic jacket 200 is able to achieve substantiallythe same flexibility and durability as clothing. Such a configuration ofthe diagnostic jacket 200 makes it possible to configure signalreceiving chips communicating with the capsule-type endoscope 200 in ahigh degree of freedom and in a high density. The diagnostic jacket 200includes a control unit 220 configured to control the entire circuit ofthe diagnostic jacket 200.

FIG. 4 is a cross section of the diagnostic jacket 200 illustrating astructure of layers of the diagnostic jacket 200. As shown in FIG. 4,the diagnostic jacket 200 has a laminated structure of two conductivesheets 210 and 212, an insulating sheet 214 providing electricalinsulation between the two conductive sheets 210 and 212, and insulatingsheets 216 and 218 for insulating each conductive sheet from theoutside. In this laminated structure, the insulating sheet 216 issituated on the subject side, and the insulating sheet 218 is situatedon the outside of the diagnostic jacket 200. Each DST chip 230 isimbedded in the laminated structure across the insulating sheet 216, theconductive sheet 212 and the insulating sheet 214. The DST chips aredistributed over the entire region of the diagnostic jacket 200.

Each of the conductive sheets 210 and 212 has flexibility andconductivity, and is formed to surround the body of the subject from achest region to an abdominal region. Each of the conductive sheets 210and 212 is made of a conductive rubber or fabric into which a conductivematerial is incorporated. The conductive sheet 210 is set at a groundlevel The conductive sheet 212 functions as a signal layer through whicha signal (i.e., an image signal from the capsule-type endoscope 100) istransmitted between the DST chips 230 in accordance with the 2D-DSTtechnology.

Each of the insulating sheets 214, 216 and 218 has flexibility and aninsulating property, and is formed of, for example, insulating rubber,an insulating film, or fabric having an insulating property. Theinsulating sheet 214 is sandwiched between the conductive sheets 210 and212 to provide electrical insulation between the conductive sheets 210and 212. The insulating sheet 216 is formed to cover the outer surfaceof the conductive sheet 212, The insulating sheet 218 is formed to coverthe outer surface of the conductive sheet 210. By an insulating propertyof each of the insulating sheets 214, 216 and 218, electrical insulationbetween the conductive layers can be maintained and electricalinsulation between each conductive sheet (210,212) and the outside(e.g., a surface of the body of the subject 1) can be maintained.

FIG. 5 is a block diagram of the DST chip 230 according to the firstembodiment. As shown in FIG. 5, the DST chip 230 includes a control unit232, an antenna 234, an A-D converter 236, a selector 238, a storageunit 240 and an interface 242. The storage unit 240 includes fourmemories 240R, 24001, 240G2 and 240B.

In order to set up the DST chips to receive the image signal from thecapsule-type endoscope 100, the control unit 220 operates to comparesignal reception levels of signals received by antennas 234 of all theDST chips 230 in the diagnostic jacket 200. Then, the control unit 220selects a DST chip 230 of which antenna 234 has the highest signalreception level, and sets the DST chip 230 having the highest signalreception level as a signal reception chip. The DST chip 230 set as thesignal reception chip operates to receive the image signal transmittedby the capsule-type endoscope 100. The diagnostic jacket 200 thus movesto a state of being able to catch the image signal from the capsule-typeendoscope 100. Since reception conditions of the image signal from thecapsule-type endoscope 100 changes with time, the control unit 220 mayoperate to conduct the comparison of signal reception levelsperiodically to select a DST chip having the maximum signal receptionlevel.

When the image signal is received by the antenna 234 of the signalreception chip, the control unit 232 executes an image signalcompression process for compressing the image signal from thecapsule-type endoscope 100. FIG. 6 is a flowchart illustrating the imagesignal compression process executed under control of the control unit232 of the DST chip 232 (the signal reception chip). The image signalcompression process terminates when power of the diagnostic jacket 200is turned to off or when the diagnostic jacket 200 moves to a statewhere no image signal is received.

The control unit 232 has a counter (i.e., a counting function) forcounting the number of horizontal synchronization signals H and pixels(pixel signals) contained in the image signal. When the control unit 232reads a vertical synchronization signal V located at a header part ofthe image signal, the control unit 232 resets the counter (i.e., thecount C_(H) of the number of horizontal synchronization signals and thecount C_(P) of the number of pixels) to zero (steps S1 and S2). Then,the control unit 232 reads the horizontal synchronization signal andincrements the count C_(H) (step S3).

When the image signal received by the antenna 234 is inputted to the A-Dconverter 236, the control unit 232 controls the A-D converter 236 toconvert the analog image signal to a digital signal (i.e., a signalrepresenting digital information) (step S4). FIG. 7 shows an example ofan image signal (i.e., a digital signal) converted by the A-D converter236. In FIG. 7, a vertical axis represents an output level of the imagesignal, and a horizontal axis represents time. The image signal shown inFIG. 7 is inputted to the selector 238 in chronological order as shownin FIG. 7,

Next, the control unit 232 executes a signal separation process toseparate each pixel signal from the image signal (step S5). FIG. 8 is aflowchart illustrating the signal separation process.

When the separation process is initiated, the control unit 232 judgeswhether the count C_(H) representing the number of horizontalsynchronization signals has an odd number (step S51). If the count C_(H)has an odd number (S51: YES), the control unit 232 executes signalseparation for the pixels arranged along an odd line in the pixel arrayon the light reception surface of the solid-state image pickup device112. More specifically, in step S52, the control unit 232 reads a pixelsignal on an odd line in the pixel array, and increments the count C_(P)by one. Then, the control unit 232 judges whether the count C_(P) has anodd number (step S53). If the count C_(P) has an odd number (S53: YES),the control unit 232 judges that the pixel signal represents an R (red)pixel and controls the selector 238 to output the pixel signal to thememory 240R of the storage unit 240 (step S54). If the count C_(P) doesnot have an odd number (S53: NO), the control unit 232 judges that thepixel signal represents a G (green) pixel and controls the selector 238to output the pixel signal to the memory 240G1 of the storage unit 240(step S55).

If it is judged in step S51 that the count C_(H) does not have an oddnumber (S51: NO), the control unit 232 executes the signal separationfor the pixels arranged along an even line in the pixel array on thelight reception surface of the solid-state image pickup device 112. Morespecifically, in step S56, the control unit 232 reads a pixel signal onan even line in the pixel array, and increments the count C_(P) by one.Then, the control unit 232 judges whether the count C_(P) has an oddnumber (step S57). If the count C_(P) has an odd number (S57: YES), thecontrol unit 232 judges that the pixel signal represents a G (green)pixel and controls the selector 238 to output the pixel signal to thememory 240G2 of the storage unit 240 (step S58). If the count C_(P) doesnot have an odd number (S57: NO), the control unit 232 judges that thepixel signal represents a B (blue) pixel and controls the selector 238to output the pixel signal to the memory 240B of the storage unit 240(step S59).

The pixel signals are thus separated from the image signal and stored inthe storage unit 240. That is, the pixel signals of R-pixels arrangedalong an odd line of the pixel array on the light reception unit of thesolid-state image pickup device 112 are stored in the memory 240R. Thepixel signals of G-pixels arranged along an odd line of the pixel arrayare stored in the memory 240G1. The pixel signals of G-pixels arrangedalong an even line of the pixel array are stored in the memory 240G2.The pixel signals of B-pixels arranged along an even line of the pixelarray are stored in the memory 240B.

Each of the memories 240R, 240G1, 240G2 and 240B has two memorysegments. Specifically, the memory 240R has memory segments SR1 and SR2.Each of the memory segments SR1 and SR2 holds data only when power issupplied. Therefore, in an initial state, each memory segment does nothold data. The memory 240G1 has memory segments SG11 and SG12, thememory 240G2 has memory segments SG21 and S022, and the memory 240B hasmemory segments SB1 and SB2. Since these memory segments SG11, SG12,SG21, SG22, SB1 and SB2 have the same configuration as those of thememory segments SR1 and SR2, explanations thereof will not be repeated.

In the following explanations on the image signal compression processshown in FIG. 6, it is assumed that an R-pixel signal is output by theselector 238. Referring back to FIG. 6, when the pixel signal (theR-pixel signal) separated by the selector 238 is outputted, the controlunit 232 judges whether memory segment SR1 of the memory 240 holds data(step S6). If the segment SR1 does not hold data (S6: NO), the controlunit 232 stores data of the R-pixel signal in the memory segment SR1(step S7). In this case, the control unit 232 uses one of memorysegments in order of precedence of the vacant memory segment, the memorysegment SR1, and the memory segment SR2 to store the R-pixel signal inthe memory 240R. After step S7 is executed, the memory 240R is in astate where only the memory segment SR1 is filled with the R-pixelsignal.

The R-pixel signal stored in step S7 is a first R-pixel signal on eachodd line on the pixel array as described below in a difference operationprocess. This first R-pixel signal is used as a reference signal for thedifference operation process. Therefore, the control unit 232 assigns anidentification (the count C_(H) of the horizontal synchronizationsignals and the count C_(P) of the pixels) to the R-pixel signal in astate where the pixel signal is not processed (step S8). Then, thecontrol unit 232 outputs the pixel signal to the interface 242 (stepS9). Then, control returns to step S4 to execute the signal separationprocess again.

If the segment SR1 holds data (S6: YES), the control unit 232 stores theR-pixel signal in the memory segment SR2 (step S10). When the R-pixelsignal is thus stored in the memory segment SR2, the memory 240R is in astate where all of the memory segments SR1 and SR2 are filled with data.It should be note that even if the memory segment SR2 is filled withdata, the control unit 232 overwrites the memory segment SR2 with theR-pixel signal in step S10.

Next, in step S11, the control unit 232 refers to the data of theR-pixel signals stored in the memory segments SR1 and SR2 to calculate adifference between the output values of the R-pixel signals in thememory segments SR1 and SR2 and thereby to generate a difference signalrepresenting the calculated difference (step S11). The difference isobtained by subtracting the value of the signal output of the memorysegment SR2 from the value of the signal output of the memory segmentSR1. It is understood that the values of the memory segments SR1 and SR2correspond to the neighboring same color pixels (i.e., the R-pixelsbetween which a G-pixel signal lies) on the pixel array on the lightreception surface of the solid-state image pickup device 112. Therefore,these same color signals have strong correlation with respect to eachother. In other words, the output value of the difference signal takes asmall value. As a result, the R-pixel signal can be compressed at a highcompression rate.

FIGS. 9A to 9F illustrate effect of the difference operation process.FIG. 9A represents output values of all the pixels on an odd line of thepixel array. FIG. 9B represents output values of R-pixels on the oddline shown in FIG. 9A. FIG. 9C represents output values of G-pixels onthe odd line shown in FIG. 9A. FIG. 9D represents output values ofdifference signals between neighboring pixels on the odd line. FIG. 9Erepresents output values of difference signals between neighboringR-pixels on the odd line. FIG. 9F represents output values of differencesignals between neighboring G-pixels on the odd line. In each of FIGS.9A to 9F, a vertical axis represents an output level of the pixel signaland a horizontal line represents pixels on an odd line on the pixelarray.

As shown in FIG. 9A, output values of neighboring R and G pixels on anodd line have low correlation because the neighboring R and G pixels aredifferent in color with respect to each other. Therefore, as shown inFIG. 9D, each difference signal has a relatively high output value. Thatis, in this case, the image signal is not effectively compressed.

On the other hand, if a difference signal is calculated from neighboringsame color pixels, an output value of the difference signal takes a lowvalue because the neighboring same color pixels have strong correlationwith each other, as indicated in FIGS. 9E and 9F. That is, in this case,the image signal is effectively compressed.

After obtaining the difference signal, the control unit 232 assigns theidentification of the R-pixel signal currently stored in the memorysegment SR2 to the difference signal (step S12), and outputs thedifference signal to the interface 242 (step S13). Then, the controlunit 232 copies the R-signal currently stored in the memory segment 8R2to the memory segment SR1 (step S14).

Next, in step S15, the control unit 232 judges whether the count C_(P)of the pixel signal is equal to n. If the count C_(P) of the pixelsignal is not equal to n (S15: NO), the control unit 232 judges that asequence of steps for all the pixels on a current line is not finished,and control returns to step S4 to execute the signal separation foranother pixel signal on the current line. If the count C_(P) of thepixel signal is equal to n (S15: YES), the control unit 232 judges thata sequence of steps for all the pixels on the current line is finished,and control proceeds to step S16.

In step 516, the control unit 232 judges whether the count C_(H) of thehorizontal synchronization signal is equal to m. If the count C_(H) ofthe horizontal synchronization signal is equal to m (S16: YES), thecontrol unit 232 judges that a sequence of steps for a current frame isfinished, and control returns to step S1 to execute the signalseparation for a next frame. If the count C_(H) of the horizontalsynchronization signal is not equal to m (S16: NO), the control unit 232judges that a sequence of steps for the current frame is not finished,and control returns to step S2 to execute the signal separation for anext line.

The interface 242 is electrically connected to the conductive sheets 210and 212. Each pixel signal provided to the interface 242 in step S9 orS13 is transmitted to the control unit 220 while passing through thesignal layer (the conductive sheet 212) and being relayed by theappropriately selected DST chips 230 which have been selected as thetransmission channel. The pixel signals are inputted to the control unit220 in the order where the pixels are arranged in the pixel array (“R,G, R, G, . . . ”).

Then, the control unit 220 decompresses each pixel signal (i.e., obtainsthe output value of each pixel signal in a state before execution of thedifference operation process) in accordance with the reference signaland difference signals of each line. The control unit 220 refers to theidentification of each pixel signal and stores a frame of decompressedpixel signals, for example, in a memory provided therein. When a frameof decompressed pixel signals is stored, the control unit 220 subjectsthe pixel signals to image processing to output a frame of image to thePC 300 with the monitor so that an image of the inside of the bodycavity of the subject 1 captured by the capsule-type endoscope 100 isdisplayed on the monitor of the PC 300.

In the above explanations on the image signal compression process shownin FIG. 6, the image signal compression for R-pixel signals are treatedfor the sake of simplicity. It is understood that G-pixel signals in anodd line, G-pixel signals in an even line, and B-pixel signals are alsocompressed in the image signal compression process in the same fashion.

As described above, by generating the difference signal usingneighboring same color pixels, the image signal can be compressed at ahigh compression rate through use of a relatively simple circuit.

Second Embodiment

FIG. 10 is a block diagram of an endoscope system 10 z according to asecond embodiment of the invention. In FIG. 10, to elements, which aresubstantially the same as those of the first embodiment, the samereference numbers are assigned, and explanations thereof will not berepeated, As shown in FIG. 10, the endoscope system 10 z includes thecapsule-type endoscope 100, a diagnostic jacket 200 z, and the PC 300with the monitor. The diagnostic jacket 200 z includes four types of DSTchips (DST chips 230R, 230G1, 230G2 and 230B). The DST chips areuniformly distributed over the entire region of the diagnostic jacket200 z.

FIG. 11 is a block diagram of the DST chip 230R. As shown in FIG. 11,the DST chip 230R includes a control unit 232 z, the antenna 234, theA-D converter 236, a selector 238R, the memory 240R and the interface242. The memory 240R includes memory segments SR1 and SR2.

Under control of the control unit 220, signal reception levels of all ofthe DST chips in the diagnostic jacket 200 z are compared so that a DSTchip having the maximum signal reception level can be selected. Thecontrol unit 220 selects the DST chip having the maximum signalreception level as a signal reception chip. In this embodiment, if theDST chip 230R is selected as a signal reception chip, the control unit220 also selects the DST chips 23001, 230G2 and 230B adjoining to theDST chip 230R as signal reception chips. If the DST chip 230G2 isselected as a signal reception chip, the control nit 220 may select theDST chips 230R, 23001, and 230B adjoining to the DST chip 230G2 assignal reception chips. That is, four types of DST chips 230R, 230G1,230G2 and 230B are selected as signal reception chips. The antenna 234of each DST chip selected as a signal reception chip operates to catchthe image signal transmitted from the capsule-type endoscope 100.

FIG. 12 is a flowchart illustrating an image signal compression processexecuted under control of the control unit 232 z of the DST chip 230R.Since each of the DST chips 23001, 230G2 and 230B has the sameconfiguration and functions as those of the DST chip 230R, explanationsthereof will not be repeated.

The control unit 232 z executes steps S1 b to S4 b which aresubstantially the same as steps S1 to S4 in FIG. 6. Then, a signalextraction process is executed in step S60. FIG. 13 is a flowchartillustrating the signal extraction process. In the signal extractionprocess, only pixel signals satisfying a predetermined condition areextracted and outputted to the memory. With regard to the DST chip 230R,the predetermined condition is a condition for selecting only R-pixelsignals. With regard to the DST chip 230G1, the predetermined conditionis a condition for selecting only G-pixel signals on each odd line inthe pixel array. With regard to the DST chip 230G2, the predeterminedcondition is a condition for selecting only G-pixel signals on each evenline in the pixel array. With regard to the DST chip 2308, thepredetermined condition is a condition for selecting only B-pixelsignals.

In the signal extraction process, the control unit 232 z judges whetherthe count C_(H) representing the number of horizontal synchronizationsignals has an odd number (step S61). If the count C_(H) has an oddnumber (S61: YES), the control unit 232 z executes signal extraction forthe pixels arranged along an odd line in the pixel array on the lightreception surface of the solid-state image pickup device 112. Morespecifically, in step S62, the control unit 232 z reads a pixel signalon an odd line in the pixel array, and increments the count C_(P) byone. Then, the control unit 232 z judges whether the count C_(P) has anodd number (step S63). If the count C_(P) has an odd number (S63: YES),the control unit 232 z judges that the current pixel signal is anR-pixel signal and controls the selector 238 to output the signal to thememory 240R (step S64).

If the count C_(P) does not have an odd number (S63: NO), the controlunit 232 z judges that the pixel signal is not an R-pixel signal andcontrols the selector 238 not to output the pixel signal to the memory240R. Then, control proceeds to step S15 of FIG. 12.

If it is judged in step S61 that the count C_(H) does not have an oddnumber (S61: NO), the control unit 232 z reads a pixel signal on an oddline in the pixel array, and increments the count C_(P) by one (stepS65). In this case, the control unit 232 z judges that the pixel signalinputted to the selector 238 is a pixel signal on an even line in thepixel array (i.e., the pixel signal is not an R-pixel signal) andcontrols the selector 238 not to output the signal to the memory 240R.Then, control proceeds to step S15 of FIG. 12.

When the R-pixel signal is output by the selector 238 in step S64, thecontrol unit 232 z stores the R-pixel signal in one of the memorysegments in the memory 240R in accordance with the status of the memorysegments, and executes the difference operation for the pixel signalsstored in the memory segments to output a result of the differenceoperation through the interface 242 as shown in steps S7 b to S9 b(which are substantially the same as steps S7 to S9 in FIG. 6) or S10 bto S14 b (which are the same as steps S10 to S14 in FIG. 6). In responseto the statuses of the count C_(H) and count C_(P), the image signalcompression process is repeated as shown in steps S15 b and S16 b whichare substantially the same as steps S15 and S16 in FIG. 6.

Since the DST chip 230R needs to output only R-pixel signals, the DSTchip 230 is required to have only the memory 240R. That is, a memorysize in each DST chip can be reduced. Such an advantage is also appliedto other DST chips (230G1, 230G2, 230B). Since, according to the secondembodiment, the memory size in each DST chip can be reduced incomparison with the DST chip in the first embodiment, and cost reductioncan be achieved.

The pixel signals of the four DST chips selected as the signal receptionchips are sequentially subjected to the image signal compression processin the order of the pixel arrangement in the Bayer array. Then, thepixel signals are transmitted to the control unit 220 while passingthrough the conductive sheet 210 and being relayed by the DST chipsselected to form the signal transmission channel in accordance with the2D-DST technology. More specifically, the reference signal of theR-pixel signal compressed in the DST chip 230R is transmitted, and thenthe reference signal of the G-pixel signal is transmitted. Subsequently,the difference signal of the neighboring R-pixel and the differencesignal of the neighboring G-pixel signal are transmitted repeatedly asshown in FIG. 7. As a result, the R and G pixel signals are inputted tothe control unit 220 as shown in FIG. 7. When a target line to beprocessed is changed, the reference signal of the G-pixel signal istransmitted and then the reference signal of the B-pixel signal istransmitted. Subsequently, the difference signal of the neighboringG-pixel and the difference signal of the neighboring B-pixel signal aretransmitted repeatedly. As a result, the G and B pixel signals areinputted to the control unit 220.

The control unit 220 decompresses each pixel signal (i.e., obtains theoutput value of each pixel signal in the state before execution of thedifference operation process) in accordance with the reference signaland difference signals of each line. When a frame of decompressed pixelsignals is stored, the control unit 220 subjects the pixel signals toimage processing to output a frame of image to the PC 300 with themonitor so that an image of the inside of the body cavity of the subject1 captured by the capsule-type endoscope 100 is displayed on the monitorof the PC 300.

Third Embodiment

Hereafter, an endoscope system according to a third embodiment isdescribed. Since a general configuration of the endoscope systemaccording to the third embodiment is substantially the same as that ofthe first embodiment, the drawings of the first embodiment are also usedto explain the endoscope system according to the third embodiment. Inthis embodiment, DST chips 230 y (see FIG. 14) are distributed over theentire region of the diagnostic jacket 200. In this embodiment, toelements, which are substantially the same as those of the firstembodiment, the same reference numbers are assigned, and explanationsthereof will not be repeated.

FIG. 14 is a block diagram of a DST chip 230 y according to the thirdembodiment. As shown in FIG. 14, the DST chip 230 y includes a controlunit 232 y, the antenna 234, the A-D converter 236, the selector 238,the memory 240Y, and the interface 242. The memory 240Y includes linememories 240 a and 240 b. Each of the line memories 240 a and 240 b hasa memory size enough to store a line of pixel signals. The line memory240 a stores pixel signals in each odd line in the pixel array, and theline memory 240 b stores pixel signals in each even line in the pixelarray.

Although in this embodiment two different line memories are provided inthe DST chip 230 y, the DST chip 230 y may be configured to have asingle line memory. If the DST chip 230 y is configured to have a singleline memory, the selector 238 operates under control of the control unit232 y to assign addresses to pixel signals such that a pixel signal at acolumn address on a line in the pixel array (i.e., to be stored in theline memory 240 a) and a pixel signal at the same column address onanother line in the pixel array (i.e., pixel signals to be stored in theline memory 240 b) have different addresses. In this case, the DST chiphaving the single line memory operates as if the DST chip has separatememory areas corresponding to the line memories 240 a and 240 b.

FIGS. 15A to 15C are explanatory illustrations for explaining the effectof a difference operation process according to the third embodiment.FIG. 15A illustrates output values of pixel signals in an (i-2)-th line(where i is a natural number larger than or equal to 3) in the pixelarray. FIG. 15B illustrates output values of pixel signals in an i-thline. FIG. 15C illustrates output values of difference signalsrepresenting differences between output values of an (i-2)-th line andoutput values of an i-th line in the pixel array. In FIGS. 15A to 15C,the vertical line represents an output level of a pixel signal, and thehorizontal line represents pixels arranged in a horizontal direction onthe solid-state image pickup device 112.

On the pixel array of the solid-state image pickup device 112, an(i-1)-th line and an i-th line have different arrangements of colorpixels. That is, one of these neighboring lines has the arrangement of“R, G, R, G . . . ”, while the other has the arrangement of “G, B. G, B. . . ”. Therefore, these lines have low correlation with each otheralthough these lines are adjacent to each other in the pixel array. Thatis, in this case, the image signal is not effectively compressed.

On the other hand, if the difference operation process is applied tolines having the same arrangement of color pixels after the signalseparation is performed for each line, the output values of differencesignals become low levels because in this case the pixels in the lineshave strong correlation with each other as shown in FIG. 15C. That is,in this case, the image signal is effectively compressed.

FIG. 16 is a flowchart illustrating an image signal compression processexecuted under control of the control unit 232 y of the DST chip 230 y.

First, the control unit 232 y executes initialization (steps S101 andS102). In step S101, 1 is assigned to “I” (line number). In step S102, 1is assigned to “J” (column number). In this stage, the control unit 232y formats the line memories. The line number “I” (I=1, . . . , m)represents a row address of the pixel array, and “J” (J=1, . . . , n)represents a column address of the pixel array. When the image signalreceived by the antenna 234 is inputted to the A-D converter 236, thecontrol unit 232 y controls the A-D converter 236 to convert the analogpixel signal of the pixel (I, J) to a digital signal D_(IJ)(step S103).

Then, the control unit 232 y stores the digital signal Du at an addressj (j=1, . . . , n) in the line memory 240 a (j=1 when a first column isprocessed). Then, the control unit 232 y outputs the digital signalD_(IJ) to the interface 242 (step S105). Next, in step S106, the controlunit 232 y judges whether the column number J is equal to n. If thecolumn number J is equal to n (S106: YES), i.e., if steps S103 to S105are executed for all the pixels in the first line, control proceeds tostep S108. If the column number J is not equal to n (S106: NO), i.e., ifat least one of the pixel signals in the first line is not subjected tosteps S103 to S105, the control unit 232 y increments the column numberJ by one (step S107). Then, control returns to step S103. By executingrepeatedly steps S103 and S104, the pixel signal of the first column isstored in the address 1 of the line memory 240 a, the pixel signal ofthe second column is stored in the address 2 of the line memory 240 a,and the pixel signal of the n-th column is stored in the address n ofthe line memory 240 a.

Next, the control unit 232 y sets the line number I for 2, and thecolumn number J for 1 (steps S108 and S109). Then, the control unit 232y controls the A-D converter 236 to converts the analog signal of thepixel (2, J) to the digital signal D_(IJ) (step S110). Next, the controlunit 232 y stores the digital signal D_(IJ) at an address j in the linememory 240 b (j=1 when a first column is processed) (step S111), andoutputs the digital signal D_(IJ) to the interface 242 (step S112).

In step S113, the control unit 232 y judges whether the column number Jis equal to n. If the column number J is equal to n (S113: YES), i.e.,if steps S110 to S112 are executed for all the pixel signals in thesecond line, control proceeds to step S115. If the column number J isnot equal to n (S113: NO), i.e., if at least one of the pixel signals inthe second line is not subjected to steps S110 to S112, the control unit232 y increments the column number J by one (step S114). Then, controlreturns to step S110.

In step S115, the control unit 232 y sets the line number I for 3. Then,the control unit 232 y sets the column number J for 1 (step S116). Next,the control unit 232 y controls the A-D converter 236 to convert theanalog signal of the pixel (I, J) to a digital signal D_(IJ) (stepS117).

Next, in step S118, the control unit 232 y judges whether the linenumber I is an odd number or an even number. If the line number I is anodd number (S118: odd), the control unit 232 y executes a differenceoperation for the digital signal D_(IJ) stored in step S117 and thedigital signal D_(IJ) stored at the address J in the line memory 240 a,and outputs the difference signal to the interface 242 (step S119).

Next, the control unit 232 y stores the digital signal Du converted instep S117 at the address J in the line memory 240 a (step S120). Thatis, the difference signal between the pixel signal of the pixel at acolumn number in the line I and the pixel signal of the pixel at thesame column in the line (I-2) previously stored in the line memory 240 ais obtained. For example, if the digital signal D_(IJ) converted in stepS117 is the pixel signal of the pixel (5,8), the line number I is an addnumber (“5”) and the column number J is (“8”). In this case, thedifference operation is executed for the current digital signal Du andthe digital signal D_(IJ) (i.e., the pixel signal of the pixel (3,8))stored at the address 8 in the line memory 240 a, and the obtaineddifference signal is outputted to the interface 242. Next, the controlunit 232 y writes the digital signal D_(IJ) converted in step S117 inthe line memory 249 a at the address 8. As described above, since theseneighboring same color pixels have strong correlation with each other,the output values of the difference signals take low values as shown inFIG. 15C,

If the line number I is an even number (S118: even), the control unit232 y executes the difference operation for the current digital signalD_(IJ) and the digital signal D_(IJ) stored at the address J in the linememory 240 b, and outputs the obtained difference signal to theinterface 242 (step S121). For example, if the digital signal D_(IJ)converted in step S117 is the pixel signal of the pixel (10,15), theline number I is an even number (“10”) and the column number J is(“15”). In this case, the difference operation is executed for thecurrent digital signal D_(IJ) and the digital signal D_(IJ) (i.e., thesignal of the pixel (8,15)) stored at the address 15 in the line memory240 b, and the obtained difference signal is outputted to the interface242. Next, the control unit 232 y writes the digital signal Du convertedin step S117 in the line memory 240 b at the address 15. As describedabove, since these neighboring same color pixels have strong correlationwith each other, the output values of the difference signals take lowvalues as shown in FIG. 15C.

As described above, according to the embodiment, the pixel signals areseparated from the image signal for each of the lines having the samecolor arrangement, and the pixel signals separated line by line arestored in the respective line memories. That is, each line having R andG pixel signals are stored in the line memory 240 a, while each linehaving G and B pixel signals are stored in the line memory 240 b.

After step S120 or S122 is processed, the control unit 232 y judgeswhether the column number J is equal to n (step S123). If the columnnumber J is equal to n (S123: YES), i.e., steps S118 to S122 arefinished for all the pixel signals in the current line, control proceedsto step S125. If the column number J is not equal to n (S123: NO), i.e.,there is a pixel signal not subjected to steps S118 to S122 in thecurrent line, the control unit 232 y increments the column number J byone (step S124). Then, control returns to step S117.

In step S125, the control unit 232 y judges whether the line number I isequal to m. If the line number I is equal to m (S125: YES), the imagesignal compression process terminates because in this case all the pixelsignals have been processed. If the column number I is not equal to m(S125: NO), the control unit 232 y increments the line number I by onebecause in this case there is a line not subjected to the image signalcompression process (step S126). Then, control returns to step S116 toprocess the next line.

In this embodiment, a parameter of a pixel to be used to distinguish oneof the two line memories from the other is information on whether adigital signal represents a pixel for an even line or an odd line. Thatis, there is no necessity to use a parameter to distinguish a pixel in agiven color in a line from another pixel in another color in the sameline.

Fourth Embodiment

Hereafter, an endoscope system according to a fourth embodiment isdescribed. Since a general configuration of the endoscope systemaccording to the fourth embodiment is substantially the same as that ofthe third embodiment, the drawings of the first and third embodimentsare also used to explain the endoscope system according to the fourthembodiment. In this embodiment, DST chips 230 x(see FIG. 17) aredistributed over the diagnostic jacket 200. In this embodiment, toelements, which are substantially the same as those of the firstembodiment, the same reference numbers are assigned, and explanationsthereof will not be repeated.

FIG. 17 is a block diagram of the DST chip 230 x. As shown in FIG. 17,the DST chip 230 x includes a control unit 232 x, the antenna 234, theA-D converter 236, the selector 238, a memory 240X, and the interface242. The memory 240X includes a difference signal memory 240 c and theline memories 240 a and 240 b. The difference signal memory 240 c storesdifference signals generated in an image signal compression processdescribed below, The difference signal memory has a memory size enoughto store a line of difference signals.

FIG. 18 is a flowchart illustrating the image signal compression processaccording to the fourth embodiment. It should be noted that the imagesignal compression process according to the fourth embodiment isconfigured as a variation of the image signal compression processaccording to the third embodiment shown in FIG. 16.

First, the control unit 232 x executes steps S101 a to S115 a (which aresubstantially the same as steps S101 to S115). Then, the control unit232 x sets a flag F to zero (step S201). The flag F is used to indicatewhether there is a difference between output of the image signal of thecurrent line and output of the image signal of a line two lines ahead ofthe current line (i.e., between outputs of the neighboring lines havingthe same color arrangement). If the flag F is 0, the output values ofthe pixel signals in one of the targeted two lines are equal to outputvalues of the pixel signals in the other of the targeted two lines. Ifthe flag F is 1, at least one of the output values of the pixel signalin one of the targeted two lines is different from the output value ofthe corresponding pixel signal in the other line of the targeted twolines.

Next, the control unit 232 x executes steps S116 a to S122 a (which aresubstantially the same as steps S116 to S122 in the image signalcompression process according to the third embodiment). En thisembodiment, the difference signal obtained in step S 119 a or S121 a isnot outputted to the interface 242, but is outputted to the differencesignal memory 240 c. The difference signals corresponding to the pixelssignals are stored at respective addresses in the difference signalmemory 240 c (i.e., difference signal of the first column is stored ataddress “1”, difference signal of the second column is stored at address“2”, . . . and the difference signal of the n-th column is stored ataddress “n”). In this storing process, the control unit 232 x overwritespixel signals of a previous line with pixel signals of the current line.

In step S202, the control unit 232 x judges whether the output value ofthe difference signal obtained in step S119 a or S121 a is “0” (i.e.,whether the output value of the current pixel signal and the outputvalue of the corresponding pixel signal in a line two lines ahead of thecurrent line are equal to each other). If the output values of thesepixel signals are not equal to each other (S202: NO), the control unit232 x sets the flag F to “1” (step S203). Then, control proceeds to stepS123 a, If the output values of these pixel signals are equal to eachother (S202: YES), control proceeds to step S123 a without changing theflag F.

In step S123 a, the control unit 232 x judges whether the column numberJ is equal to “n”. If the column number J is equal to “n” (S123 a: YES),control proceeds to step S204. If the column number J is not equal to“n” (S123 a: NO), the control unit 232 x increments the column number Jby one (step S124 a). Then, control returns to step S117 a.

In step S204, the control unit 232 x judges whether the flag F is “1”.If the flag F is “1” (S204: YES), the control unit 232 x judges that atleast one of the output values of the pixel signals in one of thetargeted two lines is different from the output value of thecorresponding pixel signal in the other of the targeted two lines. Inthis case, the control unit 232 x outputs a line of difference signalsstored in the difference signal memory 240 c to the interface 242 sothat the difference signals are transmitted another DST chip (stepS205). Then, the control unit 232 x executes steps S125 a and S126 awhich are substantially the same as steps S125 and S126 in the imagesignal compression process shown in FIG. 16.

If the flag F is “0” (S204: NO), the control unit 232 x judges that theoutput values of the pixel signals in one of the targeted two lines areequal to the output values of the corresponding pixel signals in theother of the targeted two lines (i.e., there is no difference betweenthe image signals of the targeted two lines). In this case, the controlunit 232 x outputs a notification signal indicating that output vales ofthe pixel signals in the targeted two lines are equal to each other, tothe interface 242 (step S206). Then, the control unit 232 x executessteps S125 a and S126 a.

FIGS. 19A to 19C are explanatory illustrations for explaining the casewhere the output values of the pixel signals in the targeted two linesare equal to each other. In each of FIGS. 19A to 19C, the vertical linerepresents an output level of a pixel signal, and the horizontal linerepresents pixels arranged in a horizontal direction on the solid-stateimage pickup device 112. FIG. 19A illustrates output values of pixelsignals in an (i-2)-th line. FIG. 19B illustrates output values of pixelsignals in an i-th line (i.e., the current line). FIG. 19C illustratesoutput values of difference signals representing differences betweenoutput values of the (i-2)-th line and output values of the i-th line.Since the output values of the (i-2)-th line and the output values ofthe i-th line are equal to each other, all the output values of thedifference signal are substantial zero as shown in FIG. 19C.

It should be noted that the notification signal does not representinformation concerning a line of difference signals but represents theinformation indicating that output vales of the pixel signals in thetargeted two lines are equal to each other. Therefore, the data amountof the notification signal is smaller than that of the differencesignals corresponding to one line. As a result, network traffic in thesignal channel formed between the DST chips can be reduced, andefficiency of signal transmission between the DST chips can be enhanced.

Although the present invention has been described in considerable detailwith reference to certain preferred embodiments thereof, otherembodiments are possible.

In the above mentioned embodiment, the number of pixels in a frame iscontinuously counted so that the separated pixel signals are treated indifferent fashions in accordance with the counted number of pixels.However, by obtaining a pixel address (row and column addresses) of eachpixel, it is possible to appropriately separate each pixel signal fromthe image signal in accordance with the pixel address. Theidentification information to be assigned to a reference signal or adifference signal may be information representing a pixel address ofeach pixel signal.

In the above mentioned embodiment, each memory has two memory segments.However, each memory may be configured to have more than two memorysegments. For example, the memory 240R may be provided with (n/2) memorysegments. In this case, the DST chip can execute the image compressionprocess more quickly while storing all the R-pixel signals of one linein the memory 240R without executing a copying operation as show in stepS14 of FIG. 6. That is, the image signal compression process can besimplified.

In step S15 of the above mentioned embodiment, the control unit judgeswhether a sequence of steps for one line is finished in accordance withthe count C_(P). However, such judgment may be conducted according towhether a horizontal synchronization signal H is read.

In step S16 of the above mentioned embodiment, the control unit judgeswhether a sequence of steps for one frame is finished in accordance withthe count C_(H). However, such judgment may be conducted according towhether a vertical synchronization signal V is read.

In the above mentioned embodiment, G-pixel signals in an odd line andG-pixel signals in an even line are stored in different memories(memories 240G1 and 240G2). However, a single memory for G-pixels may beused in place of the two memories 240G1 and 24002 because the signalseparation processes for even and odd lines are not concurrentlyprocessed.

In the above mentioned embodiment, the R-pixel signals, G-pixel signalsin an odd line, G-pixel signals in an even line, and B-pixel signals arestored in different four memories, respectively. However, the imagesignal compression process may be performed by two different memoriesrespectively storing pixels in an odd line and pixels in an even line.

In the above mentioned embodiment, the image signal compression isperformed for the image signal generated by the solid-state image pickupdevice 112 having a primary color filter. However, an image signalgenerated by an image pickup device having a complementary color filer(e.g., a YMCG (Yellow, Magenta, Cyan, Green) filter) may be processed.

In the above mentioned second embodiment, four DST chips are selected assignal reception chips. However, the image signal compression processmay be executed using more than four DST chips selected as signalreception chips. By increasing the number of signal reception chips,processing burden on each chip can be reduced.

In the above mentioned third embodiment, a line of pixel signals arestored in each line memory. However, two lines of pixel signals (or morethan two lines of pixel signals) may be stored in each line memory, Inthis case, two neighboring lines having the same color arrangement arestored in each line memory. Specifically, pixel signals of neighboringodd lines (e.g., fifth and seventh lines) are stored in the line memory240 a, and pixel signals of neighboring even lines (e.g., sixth andeighth lines) are stored in the line memory 240 b. The control unit 232y executes the difference operation process for each of pixel signalshaving the same column address in each line memory. In this case, dataof the image signal can be effectively compressed and the compressedsignal is outputted to the interface 242. When pixel signals of a newline are obtained, the control unit 232 y may overwrite pixel signals inone of lines having smaller values in the line memory with the pixelsignals of the new line.

This application claims priority of Japanese Patent Application No.P2005-341758, filed on Nov. 28, 2005. The entire subject matter of theapplication is incorporated herein by reference.

1. A method of compressing an image signal including a plurality ofpixel signals outputted from a pixel array in which color pixels arearranged in a predetermined array, comprising: calculating a differencebetween pixel signals of neighboring same color pixels in the pixelarray in accordance with predetermined order where the plurality ofpixel signals are outputted from the pixel array; and generating adifference signal representing the calculated difference between thepixel signals of neighboring same color pixels.
 2. The method accordingto claim 1, wherein the calculating the difference is performed for eachof the pixel signals outputted from the pixel array line by line.
 3. Themethod according to claim 1, further comprising: adding identificationinformation concerning the difference signal to the difference signal.4. The method according to claim 1, wherein the pixel signals areoutputted from the pixel array in the predetermined order such thatcolors of neighboring pixel signals successively outputted are differentfrom each other.
 5. The method according to claim 1, wherein thepredetermined array includes a Bayer, array.
 6. The method according toclaim 1, wherein the calculating the difference and the generating thedifference signal are repeated so that difference signals are generatedfor all of the plurality of pixel signals of the pixel array.
 7. Amethod of compressing an image signal including a plurality of pixelsignals outputted from a pixel array in which color pixels are arrangedin a predetermined array, comprising: separating each of the pluralityof pixel signals from the image signal in accordance with color; storingthe separated pixel signals in accordance with color; calculating adifference between pixel signals of neighboring same color pixels usingthe stored pixel signals; and generating a difference signalrepresenting the calculated difference between the pixel signals ofneighboring same color pixels.
 8. A method of compressing an imagesignal including a plurality of pixel signals outputted from a pixelarray in which color pixels are arranged in a predetermined array,comprising: separating the plurality of pixel signals from the imagesignal line by line; storing at least one line of separated pixelsignals; calculating a difference between pixel signals in neighboringlines having a same color pixel arrangement using the stored at leastone line of separated pixel signals; and generating a difference signalrepresenting the calculated difference between the pixel signals ofneighboring same color pixels.
 9. A method of compressing an imagesignal including a plurality of pixel signals outputted from a pixelarray in which color pixels are arranged in a predetermined array,comprising: separating the plurality of pixel signals from the imagesignal line by line; storing at least one line of separated pixelsignals; calculating a difference between pixel signals in a neighboringlines having a same color arrangement using the stored at least one lineof separated pixel signals; and generating a difference signalrepresenting the calculated difference if at least one of differencesignals calculated for all the pixel signals in the stored at least oneline of separated pixel signals is not zero; and generating anotification signal if all the difference signals calculated for all thepixel signals in the stored at least one line of separated pixel signalsare zero.
 10. The method according to claim 9, wherein the notificationsignal indicates that all of the difference signals calculated for allthe pixel signals in the stored at least one line of separated pixelsignals are zero.
 11. A device for compressing an image signal includinga plurality of pixel signals outputted from a pixel array in which colorpixels are arranged in a predetermined array, comprising: a signalobtaining unit configured to obtain the image signal; a signalseparation unit configured to separate each of the plurality of pixelsignals from the image signal in accordance with color; a plurality ofmemories respectively storing different color pixel signals separated bythe signal separation unit in accordance with color; and a differencesignal generation unit configured to calculate a difference betweenpixel signals of neighboring same color pixels using the pixel signalsstored in at least one of the plurality of memories and to generate adifference signal representing the difference.
 12. The device accordingto claim 11, wherein each of the memories is able to store at least twoneighboring pixel signals in the image signal.
 13. The device accordingto claim 11, wherein the difference signal generation unit calculatesthe difference between pixel signals of neighboring same color pixelsfor all the plurality of pixel signals in the pixel array line by line.14. The device according to claim 11, wherein the difference signalgeneration unit adds identification information concerning thedifference signal to the difference signal.
 15. The device according toclaim 11, wherein: the pixel array includes a Bayer array; and theplurality of memories include a first memory storing pixel signals forred pixels in an odd line in the pixel array, a second memory storingpixel signals for green pixels in an odd line in the pixel array, athird memory storing pixel signals for green pixels in an even line inthe pixel array, and a fourth memory storing pixel signals for bluepixels in an even line in the pixel array.
 16. The device according toclaim 11, wherein: the pixel array includes a Bayer array; and theplurality of memories include a first memory storing pixel signals forred pixels in an odd line in the pixel array, a second memory storingpixel signals for green pixels in odd and even lines in the pixel array,and a third memory storing pixel signals for blue pixels in an even linein the pixel array.
 17. A device for compressing an image signalincluding a plurality of pixel signals outputted from a pixel array inwhich color pixels are arranged in a predetermined array, comprising: aplurality of signal processing units respectively corresponding todifferent colors of pixels in the pixel array, wherein each of theplurality of signal processing units comprises: a signal obtaining unitconfigured to obtain the image signal; a signal extraction unitconfigured to extract pixel signals having a predetermined color fromthe image signal; and a difference signal generation unit configured tocalculate a difference between pixel signals of neighboring same colorpixels using the pixel signals extracted by the signal extraction unitand to generate a difference signal representing the difference.
 18. Adevice for compressing an image signal including a plurality of pixelsignals outputted from a pixel array in which color pixels are arrangedin a predetermined array, comprising: a signal obtaining unit configuredto obtain the image signal; a signal separation unit configured toseparate the plurality of pixel signals from the image signal line byline; a plurality of memories respectively storing different lines ofpixel signals separated by the signal separation unit; and a differencesignal generation unit configured to calculate a difference betweenpixel signals in neighboring lines having a same color pixel arrangementusing the pixel signals stored in at least one of the plurality ofmemories and to generate a difference signal representing thedifference.
 19. The device according to claim 18, wherein each of theplurality of memories is able to store a line of pixel signals.
 20. Thedevice according to claim 18, wherein the pixel array includes a Bayerarray; and the plurality of memories includes a first line memorystoring pixel signals in an odd line in the pixel array and a secondline memory storing pixel signals in an even line in the pixel array.21. A device for compressing an image signal including a plurality ofpixel signals outputted from a pixel array in which color pixels arearranged in a predetermined array, comprising: a signal obtaining unitconfigured to obtain the image signal; a signal separation unitconfigured to separate the plurality of pixel signals from the imagesignal line by line; a plurality of memories respectively storingdifferent lines of pixel signals separated by the signal separationunit; a difference calculation unit configured to calculate a differencebetween pixel signals in neighboring lines having a same color pixelarrangement the pixel signals stored in at least one of the plurality ofmemories; and a difference signal generation unit configured to generatea difference signal representing the calculated difference if at leastone of difference signals calculated for all the pixel signals of a linein the pixel array is not zero, and to generate a notification signal ifall difference signals calculated for all the pixel signals in a line inthe pixel array are zero.
 22. The device according to claim 21, whereineach of the plurality of memories is able to store a line of pixelsignals.
 23. The device according to claim 21, wherein the pixel arrayincludes a Bayer array; and the plurality of memories includes a firstline memory storing pixel signals in an odd line in the pixel array anda second line memory storing pixel signals in an even line in the pixelarray.
 24. A wearable device, comprising: a substrate including aconductive sheet and a plurality of diffusive signal-transmission chipsdistributed over the conductive sheet, wherein each of the plurality ofdiffusive signal-transmission chips comprises a device according toclaim 11, wherein the conductive layer is formed to be able to cover atleast a part of a body of a subject, wherein information on the body ofthe subject is transmitted through the substrate.
 25. A wearable device,comprising: a substrate including a conductive sheet and a plurality ofdiffusive signal-transmission chips distributed over the conductivesheet, wherein at least parts of the plurality of diffusivesignal-transmission chips form a device according to claim 17, whereinthe plurality of signal processing units are respectively provided indifferent ones of the at least parts of the plurality of diffusivesignal-transmission chips, wherein the conductive layer is formed to beable to cover at least a part of a body of a subject, whereininformation on the body of the subject is transmitted through thesubstrate.
 26. A wearable device, comprising: a substrate including aconductive sheet and a plurality of diffusive signal-transmission chipsdistributed over the conductive sheet, wherein each of the plurality ofdiffusive signal-transmission chips comprises a device according toclaim 18, wherein the conductive layer is formed to be able to cover atleast a part of a body of a subject, wherein information on the body ofthe subject is transmitted through the substrate.
 27. A wearable device,comprising: a substrate including a conductive sheet and a plurality ofdiffusive signal-transmission chips distributed over the conductivesheet, wherein each of the plurality of diffusive signal-transmissionchips comprises a device according to claim 21, wherein the conductivelayer is formed to be able to cover at least a part of a body of asubject, wherein information on the body of the subject is transmittedthrough the substrate.
 28. An endoscope system, comprising: acapsule-type endoscope having a form of a capsule; and a wearable deviceaccording to claim 24, wherein the capsule-type endoscope includes: animage pickup unit configured to obtain an image of an inside of a bodycavity of the subject and to generate an image signal representing theobtained image; and a wireless communication unit configured to transmitthe image signal as a radio signal, wherein the signal obtaining unit inthe wearable device includes an antenna which receives the image signaltransmitted from the wireless communication unit of the capsule-typeendoscope.
 29. An endoscope system, comprising: a capsule-type endoscopehaving a form of a capsule; and a wearable device according to claim 25,wherein the capsule-type endoscope includes: an image pickup unitconfigured to obtain an image of an inside of a body cavity of thesubject and to generate an image signal representing the obtained image;and a wireless communication unit configured to transmit the imagesignal as a radio signal, wherein the signal obtaining unit in thewearable device includes an antenna which receives the image signaltransmitted from the wireless communication unit of the capsule-typeendoscope.
 30. An endoscope system, comprising: a capsule-type endoscopehaving a form of a capsule; and a wearable device according to claim 26,wherein the capsule-type endoscope includes: an image pickup unitconfigured to obtain an image of an inside of a body cavity of thesubject and to generate an image signal representing the obtained image;and a wireless communication unit configured to transmit the imagesignal as a radio signal, wherein the signal obtaining unit in thewearable device includes an antenna which receives the image signaltransmitted from the wireless communication unit of the capsule-typeendoscope.
 31. An endoscope system, comprising: a capsule-type endoscopehaving a form of a capsule; and a wearable device according to claim 27,wherein the capsule-type endoscope includes: an image pickup unitconfigured to obtain an image of an inside of a body cavity of thesubject and to generate an image signal representing the obtained image;and a wireless communication unit configured to transmit the imagesignal as a radio signal, wherein the signal obtaining unit in thewearable device includes an antenna which receives the image signaltransmitted from the wireless communication unit of the capsule-typeendoscope.